1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming system and a lubricant amount adjusting method.
2. Description of Related Art
In an image forming apparatus using an electrophotographic scheme, a cleaning device of a blade-cleaning type is known in which a plate-shaped cleaning blade composed of an elastic body and serving as a device for removing remaining toner such as untransferred toner and transfer residual toner on an image bearing member (for example, photoconductor) is brought into contact with the surface of the image bearing member to thereby remove the remaining toner on the image bearing member, for example.
In recent years, reduction of toner particle size has been demanded from the view point of enhancing the image quality, and for such a purpose, polymerization methods such as an emulsion polymerization method and a suspension polymerization method have been utilized, for example. As the size of the toner particle decreases, however, the attaching force between the toner particle and the image bearing member increases, thus reducing the ease of removal of the remaining toner on the image bearing member. In particular, when a so-called polymerization toner produced by a polymerization method is used, the toner particles have a substantially spherical shape, and as a result cleaning failures in which the toner particles roll on the image bearing member and slip through the cleaning blade are easily caused, thus further reducing the ease of removal of the remaining toner on the image bearing member.
In addition, when toner slips through the cleaning blade, the toner becomes the core of toner aggregate formed on the image bearing member, and grain blank (raindrop) is generated on the solid image printing part. To solve such a quality problem as the above-mentioned “raindrop” today, lubricant (e.g., metal soap of metal stearate) is supplied onto the image bearing member to form coating of the lubricant such that cleaning is performed in the state where the attaching force between the toner particle and the image bearing member is suppressed to a low level. Examples of the mechanism for supplying lubricant on the image bearing member include a lubricant application process in which a brush is brought into contact with lubricant formed in a rod shape to scrape the lubricant and supply the lubricant to the surface of the image bearing member, a toner adding process in which a toner image is formed with use of toner containing lubricant-external additive (lubricant) to supply the lubricant or a process combining the lubricant application process and the toner adding process.
The image forming apparatus provided with the lubricant supply mechanism supplies lubricant onto the surface of the image bearing member and thereby reduces a frictional coefficient with respect to the toner on the surface of the image bearing member. When transferring the toner image formed on the surface of the image bearing member to a transfer member (e.g., intermediate transfer belt), this makes it possible to suppress the occurrence of transfer failures and improve the image quality of the toner image. It is also possible to reduce the frictional coefficient between the cleaning blade or the like brought into pressure-contact with the image bearing member and the image bearing member, and thereby suppress shaving (abrasion) of the surface layer of the image bearing member, and eventually extend the service life of the image bearing member.
For example, Japanese Patent Application Laid-Open No. 2011-112665 discloses a toner removing section configured to dispose a cleaning brush on an upstream side of a cleaning blade in a rotational direction of an image bearing member and remove remaining toner before reaching the cleaning blade using the cleaning brush.
An insufficient amount of lubricant coated onto the image bearing member may produce problems such as cleaning failures, granular noise, stripe image irregularity, and on the other hand, an excessive amount of lubricant may produce problems such as reduction of durability of the cleaning blade due to adhesive wear and image degradation due to mixture of lubricant from the developing section to the developer, and therefore an appropriate amount exists for the amount of lubricant. Moreover, a difference in the amount of lubricant may produce unevenness in image concentration or image quality, and it is therefore necessary to maintain the amount of lubricant stably and to within an appropriate range in order to stabilize the image concentration or image quality.
The toner adding process does not require a coating device such as a lubricant rod and a brush, and therefore is advantageous in terms of installation space and cost. In the toner adding process, however, the amount of the lubricant in the developing device varies depending on the amount of toner consumption, and as a result the amount of the lubricant to be applied onto the image bearing member varies. The amount of the lubricant to be coated onto the image bearing member is determined by a balance between the “supply amount” of the lubricant supplied onto the image bearing member and the “collection amount” of the lubricant scraped and collected after being supplied onto the image bearing member. In the toner adding process, since the lubricant is supplied from a developer, when a high coverage image is printed, the supply amount of the lubricant increases, whereas when a low coverage image is printed, the supply amount of the lubricant decreases. Originally, the lubricant is supplied only to parts on the image bearing member to which toner is supplied. However, there is actually lubricant which detaches from toner and becomes independent as well due to the influence of a load during stirring in the developing device and an electric field load in a transfer section (development region), and the lubricant is also supplied to a white base where there is no image.
On the other hand, the cleaning blade which is in contact with the image bearing member has a large effect on the amount of lubricant collected and the lubricant is scraped and collected by a friction with the toner (mainly external additive component) blocked by a blade edge section at which the cleaning blade is in contact with the image bearing member. Furthermore, the amount of lubricant collection varies depending on the amount of toner supplied to the blade edge section as well, the greater the amount of toner supplied, the greater the amount of lubricant collected becomes, whereas the smaller the amount of toner supplied, the smaller the amount of lubricant collected becomes. That is, the amount of lubricant collection increases when a high coverage image is printed and the amount of lubricant collection decreases when a low coverage image is printed.
As described above, the relationship between the supply and collection of lubricant varies depending on the coverage of an image to be printed, and by extension, there is a difference in the amount of lubricant coated onto the image bearing member depending on the ratio of the supply and collection, resulting in a problem in that it is not possible to maintain the amount of lubricant coated onto the image bearing member to within an appropriate range.
Note that the technique according to Japanese Patent Application Laid-Open No. 2011-112665 is a technique for reducing the amount of toner supplied to the blade edge section and is not a technique for preventing the occurrence of a difference in the amount of lubricant coated onto the image bearing member depending on the coverage of an image to be printed. That is, the technique described in Japanese Patent Application Laid-Open No. 2011-112665 is not intended to maintain the amount of lubricant coated onto the image bearing member to within an appropriate range, and thus does not have the configuration therefor.